One of the most incredible things about photovoltaic power is its simplicity. It is almost completely solid state, from the photovoltaic cell to the electricity delivered to the consumer. Whether the application is a solar calculator with a PV array of less than 1 W or a 100 MW grid-connected PV power generation plant, all that is required between the solar array and the load are electronic and electrical components.
Compared to other sources of energy humankind has harnessed to make electricity, PV is the most scaleable and modular. Larger PV systems require more electrical bussing, fusing and wiring, but the most complex component between the solar array and the load is the electronic component that converts and processes the electricity: The Solar Inverter.
In the case of grid-tied solar system, the inverter is the only piece of electronics needed between the array and the grid. But Off grid solar system: applications use an additional DC to DC converter between the array and batteries and an inverter with a built-in charger.
5 things you need to consider before choosing Solar Inverter for your home solar PV system:
- How do Solar Inverters work?
- Types of Solar Inverter
- What size should you buy
- How much should you spend for Solar Inverter
- What Solar Inverter brands?
First, let talk a little bit about how does it work?
#1 How do Solar Inverters work?
DC to AC
The Power Inverter is what changes the direct current (DC) from your battery to alternating current (AC) needed by many electrical devices. If you are going to run just simple 12 volt DC (direct current) devices off your batteries, then you won’t need it. However, most of us will need to run AC equipment.
See the image below to know the basic difference between DC and AC:
In a wire with AC, the electricity is running in one direction and then the other thus “alternating” its direction. The smoothness with which this current flows is described by a “sine wave” where, if you were watching electrons flow from one point in the wire, they might appear to go first one way and then the other.
DC electricity, on the other hand, is flat because there is no wave, no alternation between positive and negative.
DC flows only in one direction. And story end!
With AC, however, there is a bit more to tell. The stuff that the power companies send me doesn’t flow just one way; it reverses its direction 60 times every second. (That’s why they call it 60 cycles per second.)
So, The inverter work like a magic. OK, now I think you really understood the difference between DC and AC, and how do solar inverters work in our PV system.
#2 Types of Solar Inverter
Standard string inverter warranties are usually between 5 and 10 years; as this is less than the warranties on solar PV panels it would seem sensible to budget for at least one string inverter replacement during the lifetime of your solar PV system. If you have micro-inverters installed instead this may not be necessary.
A string inverter works most efficiently when all the solar PV panels have the same characteristics and are operating under the same conditions. If it is known from the start that some of the panels are not likely to be operating under the same conditions.
For example, they are not all orientated in the same direction or some of them will be shaded for a part of the day – this would be a good reason to install two or more inverters as part of the system.
An alternative would be to install an inverter that has been designed to cope with more than one string of solar PV panels operating in different conditions.
Micro-inverters get around the need for all panels to have the same characteristics and be operating under the same conditions by having an inverter installed to the back of each panel. This means when the performance of a panel is affected, for example by natural shading or from obstructions from leaves or debris, it will not affect the overall performance of the system, as would a string invertor – particularly one without MPPT.
Micro-inverters also include MPPT which micro-inverter manufacturers claim works more effectively than it does in string inverters where something as small as an antenna could reduce the performance of the whole solar PV system.
Some benefits of micro-inverter that I want you know
- Performance of the solar PV array is optimized and reports claim the system could have improved energy harvest of between 5 per cent and 20 per cent over the lifetime of the system
- Improved energy harvest should result in increased income
- The potential for enhanced monitoring as the performance of each individual panel can be monitored separately
- Greater reliability – if one micro-inverter fails, it will not affect the whole PV system
- Installation of micro-inverters is cheaper and easier as wiring is simpler and no high voltage DC equipment is required, which also makes them safer to install.
- It may be easier to increase system size by adding new panels.
- Increased lifetime – the single most common cause of failure in a solar PV system is the string invertor, which normally requires replacement at least once over the lifetime of the array. The latest micro-inverters have fewer life-limited components, and manufacturers claim a lifetime of 25 years to match the panels
- The cost per watt is more for micro-inverters but is offset by a simpler installation and increased energy harvested.
Drawbacks of micro-inverters
- Still a relatively new technology and there are only a small number of manufacturers
- More expensive than string invertors
- Potentially costly to replace as roof access required
- Only useful in situations where shading is a significant issue
- Lack of expertise should things go wrong – relatively small market thus reliance on small pool of installers and manufacturers
OFF-grid solar inverter
Off grid solar inverter are already multitaskers: combination inverter/chargers with bi-directional energy capabilities to convert DC to AC and AC to DC. This allows the inverter to manage PV or other energy sources while also maintaining battery storage.
Until recently, the rather clean-cut separation between off-grid solar PVsystems (mainly for providing power in remote or stand-alone applications without grid access) and grid-tied systems (mainly to supplement utility power for economic reasons) made it easy to segregate solar inverters into two related classes, with little or no overlap between them.
#3 What size should I buy?
General Steps to Size an solar Inverter
There are three basic steps you have to take to figure out the wattage ratings for the inverter you will need:
1.Calculate the Continuous Loads: Add up all the normal operating wattages of the equipment you expect to be running simultaneously.
2.Calculate the Surge Loads: Add up all the surge or peak wattages of the equipment that might possible be starting at the same time.
Warning! When sizing an inverter for a system, the safest way to do it is to look up the surge loads for all the equipment you are likely to be running. Some devices such as pumps, refrigerators and air conditioners can have surge power demands 3 to 7 times their continuous power ratings. It is extremely important to know this because startup loads can be very high if they occur simultaneously and it can trip the circuit breaker in your inverter.
3.Adjust for Inverter inefficiency: As with a lot of electrical equipment, there is some loss of power.
Pure Sine Wave Inverter loses about 10%.
Modified Sine Wave Inverter loses about 15%.
The key to choosing the right size
There are many different makes and sizes of inverters on the market. The key are:
- Maximum amount of DC electricity (expressed as max DC power in Watts) the maximum number of watts the inverter has been designed to convert
- Maximum input voltage – this is the maximum voltage the inverter can manage before its electronics are damaged
- Initial input voltage (sometime called start-up voltage) – the minimum number of volts the solar PV panels need to produce for the inverter to start working
- Maximum power point (mpp) voltage rang – the voltage range at which the inverter is working most efficiently.
Many solar PV systems in the US have an inverter with a power rating that is smaller than the array. For a 3kWp array, this equates to an inverter size of between 2.4kW and 3.3kW (often expressed in watts: 2400W to 3300W). This is because the panels are not likely to be generating at their rated efficiency for long periods of time, and to ensure that the initial input voltage and maximum power point voltage range are reached as often as possible.
Inverter manufacturers often provide guidance to installers on solar inverter sizing, typically through providing system sizing software. As each inverter is manufactured to cope with a pre-determined maximum input voltage, the final choice of inverter will also be influenced by what is available on the market, particularly if your installer prefers to work with a limited number of makes.
#4 How much should I spend for a solar inverter
This is a difficult question to answer, as grid connected inverters are mostly offered as part of a solar PV system package. The inverter can represent around 20% of the cost of a system.
You can easily check out the price of solar inverter in the US by go into website of Wholesalesolar.com
But whatever you do: Never buy the cheapest inverter on the market! The real el cheapo inverters have no chance of lasting 15 years plus. Trust me on this. It is hard to design and make a good inverter that will last. Never buy a bottom of the range inverter from a no name brand. It is false economy. It just won’t last (rather like the companies selling them!).
#5 What solar inverter brands?
I recommend some options for you.
- Safe and efficient
- Product from German company
- Legendary quality
- Long and proud history
- But expensive
- Top quality
- Product from European
- Lots of features
- Great performance
- Huge company
- Popular in Europe
- Good quality, good support
- Upper mid range
- Low risk buy
Delta energy system:
- Build like a tank
- European heritage
- Long history
- Good for money
- Good support
- Good budget option
- High efficiency